1. Field of the Invention
This invention relates to photolithographic techniques used for lithography processes in the manufacture of semiconductor devices, and more particularly to exposure masks using the phase shift effect and a manufacturing method thereof.
2. Description of the Related Art
With the recent advances in semiconductor technology, semiconductor devices have been made faster and more highly integrated, giving rise to the need of making pattern dimensions much finer and more accurate. To meet these requirements, short wavelength light, such as far ultraviolet light, has come to be used as an exposure light source. In recent years, attempts to make pattern dimensions finer without changing an exposure light source have been made. One approach in the attempts is a phase shift method. The approach is such that a phase-inverted layer (phase shifter) is provided partially at a light transmission section to remove an adverse effect of diffraction occurring between adjacent patterns, thereby improving the pattern accuracy.
One phase-shift approach by which resolution is particularly improved is the Levenson-type phase shift method (Jpn. Pat. Appln. KOKAI Publication No. 62-50811). With this approach, phase shifters are provided alternately on the light transmission section in a mask on which a shading pattern is provided. The phase of the light passing through a phase shifter is inverted by 180.degree. with respect to the light passing through a portion where a phase shifter is not provided. Inverting the phase of light at the adjacent transmission sections this way causes negative interference of light between the patterns, thereby improving the resolution.
One known method of manufacturing Levenson-type phase shift masks is the approach of making a mask by digging a substrate (Jpn. Pat. Appln. KOKAI Publication No. 62-189468). Masks using the approach of digging a substrate, however, have a problem: even if the dimensions of the opening are the same, the phase shift section where the substrate is dug differs from the non-phase shift section where the substrate is not dug in the intensity of light. The problem arises from the fact that the dimensions of the opening are optically narrowed by the interference of the pattern edge portion parallel to the optical axis at the phase shift section.
To solve the problem, the adjustment of the desired exposure has been made by adjusting the dimensions of openings in a pattern of a conventional exposure mask. Such adjustment by the dimensions of openings, however, is liable to be restricted by the pattern. For instance, the desired opening width cannot be obtained, depending on the size of adjacent patterns.
As described above, since the Levenson method-applied pattern differs from the Levenson method-unapplied pattern in the desired exposure in a conventional Levenson-type phase shift mask and the adjustment of the desired exposure is made by adjusting the dimensions of openings in a pattern, the pattern has imposed restriction on the adjustment. For instance, the desired opening width cannot be provided, depending on the size of adjacent patterns.
The object of the present invention is to provide an exposure mask capable of adjusting the desired exposure for Levenson method-applied patterns and Levenson method-unapplied patterns without being restricted by the patterns and a manufacturing method thereof.